{"record":{"id":"4919c8ae0c6b9ce1","repo":"vitessio/vitess","slug":"failed-to-get-schema-from-tablet-v-err-v","errorCode":null,"errorMessage":"failed to get schema from tablet %v. err: %v","messagePattern":"failed to get schema from tablet (.+?)\\. err: (.+?)","errorType":"console","errorClass":null,"httpStatus":null,"severity":"error","filePath":"go/vt/vtctl/schematools/diff.go","lineNumber":48,"sourceCode":"\n// CompareSchemas returns (nil, nil) if the schema of the two tablets match. If\n// there are diffs, they are returned as (diffs []string, nil).\n//\n// If fetching the schema for either tablet fails, a non-nil error is returned.\nfunc CompareSchemas(\n\tctx context.Context,\n\tts *topo.Server,\n\ttmc tmclient.TabletManagerClient,\n\tsource *topodatapb.TabletAlias,\n\tdest *topodatapb.TabletAlias,\n\ttables []string,\n\texcludeTables []string,\n\tincludeViews bool,\n) (diffs []string, err error) {\n\treq := &tabletmanagerdatapb.GetSchemaRequest{Tables: tables, ExcludeTables: excludeTables, IncludeViews: includeViews}\n\tsourceSchema, err := GetSchema(ctx, ts, tmc, source, req)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"failed to get schema from tablet %v. err: %v\", source, err)\n\t}\n\n\tdestSchema, err := GetSchema(ctx, ts, tmc, dest, req)\n\tif err != nil {\n\t\treturn nil, fmt.Errorf(\"failed to get schema from tablet %v. err: %v\", dest, err)\n\t}\n\n\treturn tmutils.DiffSchemaToArray(\"source\", sourceSchema, \"dest\", destSchema), nil\n}\n","sourceCodeStart":30,"sourceCodeEnd":58,"githubUrl":"https://github.com/vitessio/vitess/blob/01a25a7d176f94613b8d59d799f438380a8760e4/go/vt/vtctl/schematools/diff.go#L30-L58","documentation":"CompareSchemas fetches the schema of the SOURCE tablet via GetSchema (an RPC to its tabletmanager) and wraps any failure with this message identifying the source tablet alias. It means the schema could not be retrieved, so the diff cannot proceed and the whole call returns an error.","triggerScenarios":"Calling CompareSchemas (directly or via CopySchemaShard) where `GetSchema(ctx, ts, tmc, source, req)` fails: source tablet alias invalid/not in topo, tablet unreachable, or the GetSchema RPC returns an error (e.g. MySQL error reading information_schema, permission denied).","commonSituations":"CopySchemaShard run with a misspelled or dead source tablet/shard alias; source tablet's mysqld down; vttablet lacking MySQL privileges to read schema; tablet was recommissioned under a different alias.","solutions":["Verify the source tablet alias is valid and serving: `vtctldclient GetTablets`.","Run `vtctldclient GetSchema <source-alias>` manually to see the underlying RPC/MySQL error.","Check the source tablet's vttablet and mysqld are running and reachable.","Fix MySQL grants for the vttablet user if the inner error indicates access denied."],"exampleFix":"// before: failing call\nCompareSchemas(ctx, ts, tmc, badAlias, dest, tables, excludeTables, includeViews)\n// after: validate alias first\nif _, err := ts.GetTablet(ctx, source); err != nil { return fmt.Errorf(\"source tablet %s not found: %w\", source, err) }","handlingStrategy":"validation","validationCode":"if _, err := ts.GetTablet(ctx, source); err != nil {\n  return fmt.Errorf(\"source tablet %s unavailable: %w\", source, err)\n}","typeGuard":null,"tryCatchPattern":"if err := compareSchemas(...); err != nil {\n  if strings.Contains(err.Error(), \"failed to get schema from tablet\") {\n    log.Errorf(\"schema fetch failed; verify tablet is serving: %v\", err)\n  }\n}","preventionTips":["Validate tablet aliases with GetTablets before running CopySchemaShard/CompareSchemas.","Confirm both tablets are SERVING and their mysqld is up.","Keep vttablet MySQL grants sufficient to read information_schema.","Check tablet health after maintenance windows before schema operations."],"tags":["schema","grpc","tablet","topo"],"backgroundTag":"schema-fetch-failed","analyzedSha":"01a25a7d176f94613b8d59d799f438380a8760e4","analyzedAt":"2026-09-01T17:28:30.605Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-08T10:18:20.063Z"}